Refining alloys of lead and tin



' Patented May 31, 1938 REFINING ALLOYSOF LEAD AND TIN Jesse 0. Betterton and Yurii E. Lebedeif, Metuchen, N. J.,4 assignors to American Smelting and Refining Company, New York, N. Y., a

corporation of New Jersey Application April 17, 1937, Serial No. 137,426

10 Claims.

This invention relates to the art of reiining alloys of lead and tin, such as solders and similar white metalcompositions, with zinc and alkalinereacting reagents. l

It is known to rene a lead-tin alloy by incorporting zinc in a molten bath of lthe alloy thereby producing a zinc dross containing the bulk of the impurities (As, Cu, Ni, Sb, precious metals, etc.) originally present in the alloy". 'I'his dross may be pressed and separated from the bath, the latter cooled to approximately its freezing point and the cooling drosses and crusts removed whereupon it will be found that the bath still contains between 1% and 1.5% antimony in addition to 4% to 5% zinc.

It is also known to reiine lead-tin alloys with alkaline-reacting metals, which term is 'used herein as consisting of members of the alkali and alkaline earth groups, magnesium and aluminum. They may be introduced into the bath either in elemental or suitable alloy form and function in a manner similar to that described with reference to zinc, i. e.; by forming a dross containing the impurities which can be separated from the bath. As thesev alkaline-reacting metals are more eilicacious than zinc in removing l antimony from. lead-tin alloys, they may be successfully employed in the further reiining of alloyswhich have been subjected to a partial refining with zinc as well as in the reiining of those alloys which have not been subjected to the zinc treatment.

The present invention provides certain improvements in the refining of llead and tin alloys yield of marketable end products is obtained with.

40 a minimum loss both of reagent and metal y treated.

The invention further consists in the new and` y novel features of operation and the new and original arrangements and combinations of steps 45 in the process hereinafter described and more particularly set forth in the claims.

I'he drawing accompanying and forming part of this specification is a flow sheet illustrating the process ofthe invention.

The invention, its objects and advantages, will be more fully appreciated and understood from the following detailed description of how the invention may be practiced.

The metal to be refined, which may comprise any impure alloy of lead and tin, is melted in an ordinary v cast iron refining kettle equipped with the usual type of mechanical stirring apparatus.

When the bath has been brought to a proper temperature, for example, 830 F., a quantity of with zinc and alkaline-reacting metals which metallic zinc in slight but denite stoichiometri-- cal excess of the impurities is incorporated in the bath. The resulting dross which contains the bulk of the impurities is pressed, removed from the bath and distilled thereby recovering metallic zinc and an'impure metal'which may be further processed for the recovery of tin and other constituents. The zinc recovered from the distillation of the pressed dross is returned to the process for the treatment of additional quantities of impure alloy.

Following removal of the zinc dross, the bath is cooled to within a few degrees of its freezing temperature, the drosses and crusts resulting fromthis operation being separated from the bath. These cooling down drosses and`crusts are high in zinc and are returned to the process for the treatment of additional quantities of impure alloy.

At the conclusion of the zinc refining step just described, the bath will contain roughly 1.3% antimony and about 4% to 5% zinc. VIn order to further deantimonize the bath, it is reheated l and a suitable amount of' alkaline-reacting metal incorporated therein.

'I'he alkaline-reacting metal may be added either in elemental or alloy form and in a variety of manners. In the case oi such alkalinereacting metals as calcium, aluminum and magnesium, it is advantageous to add the reagent as a zinc alloy. If the alkaline-reacting metal is added in elemental form and is of a readily combustible nature, such as sodium, care must be taken to preclude its burning on the surface of the bath before it has had an opportunity to bei come incorporated thereinx In any event, however, the use of a cover slag is unnecessary as the manner of adding the reagent can be selected in the light of its characteristics. Thus, the reagent may be incorporated in the bath by submergence in a perforated basket or other retaining means, or it may be introduced into the bath via the vortex of the mixing machine. A

`Upon incorporation of the alkaline-reacting metal in the bath, there is formed a dross in which substantially all of the antimony and other residual impurities are concentrated. This dross isseparated from the bath and the latter, which is substantially free from antimony but which l contains some residual alkaline-reacting metal, is treated with zinc chloride. The zincchloride reactswith the residual alkaline-reacting metal in the bath to form an alkaline-reacting metal chloride-zinc chloride slag in which form it is separated from the bath.

vThe bath contaminated only with residual zinc is next treated with chlorine gas to convert the zinc to zinc chloride in which form it is separated from the refined metal.

I'he zinc chloride produced at the lbeginning and at the end of the chlorine treatment is of an impure grade being contaminated at the outset with oxychlorides vand at the end with heavy metals. Accordingly, these yields of impure zinc chloride are collected separately, combined and 5 returned to the process, as indicated in the iiow sheet, for removing the residual alkaline-reacting metaLfrom the bath. 'Ihe zinc chloride produced between the two periods just mentioned may be marketed directlyy or following a simple rening operation for the removal of whatever small amounts of heavy metals it may contain.

The alkaline-reacting metal dross upon separation from the bath is melted under a slag containing zinc chloride, preferably with sodium chloride in eutectic proportions. As indicated by the flow sheet, the alkaline-reacting metal chloride-zinc chloride slag is utilized in the treatment of said dross. By reaction of the zinc chloride with the alkaline-reacting metal of the dross there is produced a chloride of the alkaline-reacting metal and zinc, the latter entering the metal formed by the fusion of dross. 'Ihe resulting slag, consisting principally of alkalinereacting metal chloride together with the sodium chloride and excess zinc chloride and free from tin and lead, may be discarded while the metal comprising tin, lead, zinc and antimony is returned to the original kettle for treatment with additional quantities of impure alloy entering the process.

It will be appreciated that one of the features oi' the invention is the manner in which the alloy is iinally deantimonized by an alkaline-reacting metal reagent practically without loss of the alloy constituents. The eiiiciency of the process in treating the alkaline-reacting metal dross with zinc chloride whereby the tin and lead are recovered practically in toto and returned to the process is illustrated by the follow- 40 ing specific examples in which the composition of the particular alkaline-reacting metal dross, the composition of the discard slag and the analysis of the metal recovered and returned to the process are 'set forth in Columns 1, 2.a.nd 3

of the 'rabies I-Iv.

Example I-Sodum Ten parts by weight ofthe sodium dross were treated with 1 part by weight of zinc chloride by graduallyv adding the dross to the molten zinc chloride within a temperature range of 900 F. to 1000 F. The charge was mixed for approximately 10 minutes at about 950 F. following which the slag (1 part by weight) was skimmed and discarded leaving 10 parts by weight of metal of 950 F. to 1000 F. Following a mixing period oi.' approximately 15 minutes within a tem- .perature range of 950 F. to 1020 F., thevslag (1.8 parts by weight) was removed and discarded, leaving 10.1- parts by weight of metal 5v for return to the process as indicated on the iiow sheet.

Example 3 --Magnesum Ten parts by weight of the magnesium dross were added to 1.5 parts by weight of zinc chloride and 0.4 part by weight of sodium chloride, the dross being added to the fusion at a tem- 25 perature of about 950 F. to 1000 F. Upon mixing for l0 minutes, the slag (1.6 parts by weight) was skimmed leaving 10.3 parts by weight of metal for return to the process.

Table III 30 Alkaline-reacting metal (MQMSS :Discard slag Metal returned 35 Example 4-Aluminum Ten parts by weight of the aluminum dross were treated with 2.0 parts by weight of zinc 45 chloride together with 0.5 part by weight of sodium chloride. The dross was added to the A fused salt at a temperature of approximately 950 F. to 1000 F. and mixed for 'about 15 minutes, the mixing being accompanied by consid- 50 erable evolution'of fumes of aluminum chloride. Upon separation of the discard slag, there remained 10.6 parts by weight of metal for recirculation in the process.

55 suitable for return to the process for treatment Table 1V with additional batches of impure alloy.

Table I 1 v 2 Y a 60 1 2 3 lllln'g Discard slag Metal returned .ukalin i' metal (raarlgg Discard slag Metal returned A101' Naciy NaCl -38.

`Example z-czcmm Ten parts by weight of the calcium dross were treated with 1.5 parts by weight of zinc chloride From the foregoing description, it will be apparent that the invention provides a process for 70 refining impure lead-tin alloys with zinc and alkaline-reacting metals in which the various drosses Vand intermediate reaction products are utilized and recycled in a highly efficient manner. Further, while various specmc disclosures have .beenl made for the purpose of illustrating the invention, it willbe understood that various omissions, substitutions and changes may be solder contaminated with antimony which'comprises eliminating a portion of the antimony as a zinc dross, eliminating the remaining antimony as an alkaline-reacting metal dross, recovering and recycling zinc from the zinc dross for treating additional quantities of impure solder, treating the alkaline-reacting metal dross with zinc chloride to produce a discard slag and solder metal. containing antimony and zinc, returning said solder metal for treatment with additional quantities of impure solder, eliminating residual alkaline-reacting metal from the bath as an alkaline-reacting metal chloride-zinc chloride slag and utilizing same in the treatment of the alkaline-reacting metal dross, eliminating residual zinc from the bath as zinc chloride and recycling at least a portion of the zinc chloride for either eliminating residual alkaline-reacting metal from the bath or treating alkaline-reacting metal dross.

2. In deantimonizing an alloy of lead and tin with Zinc and alkaline-reacting metals whereby the antimony is removed in part as a zinc dross and in part as an alkaline-reacting metal dross, the improvement which consists in treating the alkaline-reacting metal dross with a salt fusion comprising zinc chloride thereby producing a lead-tin free slag and a lead-tin metal containing antimony and zinc suitable for return to the process for treatment along with additional quantities of alloy.

3. The process' for'treating antimony-bearing solder which comprises partially deantimonizing said solder with zinc, further deantimonizing said solder with an alkaline-reacting metal, removing residual alkaline-reacting metal from the deantimonized solder with zinc chloride and thereafter removing residual zinc from the dealkalinized solder as zinc chloride.

4. The process according to claim 3 inhWhi-chA the Ezine chloride produced in removing the residual zinc is recycled and utilized in'removing residual alkaline-reacting metal from deantimonized solder. f

5. The process for treating an impure alloy of lead or tin contaminated with antimony which and an antimony-zinc-bearing metal adapted to be recycled through the process. Y

6. The process for treating an impure alloy of lead or tin containing relatively large amounts of antimony which comprises incorporating sufiicient zinc therein to remove a portion of the antimony while leaving substantial amounts of residual -zinc in the resulting partially reiined alloy, effecting a separation of an antimonial zinc dross from the bath, treating said dross for recovering the zinc therefrom, returning the recovered zinc to the process for treating further qauntities of impure alloy, treating the `partially refined, zinc-containing bath with asuiiicient quantity of an alkaline-reacting metal to further deantim'onize the bath, effecting a separation from the. bath of an antimonial alkalinel reacting metal-zinc-bearing dross, removing this fl. The process for treating an impure alloy of lead ortin containing relatively large amounts of antimony which comprises incorporating suiiicient zinc into the alloy to remove a portion of the antimony While leaving substantial amounts of residual zinc inthe resulting partially refined alloy, eiecting a separation of an antimonial zinc dross from the bath, treating said dross for re` covering the zinc therefrom, returning the recovered zinc to the) process for treating further quantities of impure metal, treating the partially refined, zinc-containing bath with a sumcient quantity of an alkaline-reacting metal to remove the'residual antimony from the bath, eecting a separation from the bath of an antimonial alkaline-reacting metal-zinc-bearing dross, removing the dross from the bath, treating both bath and dross with zinc chloride thereby removing residual alkaline-reacting metal from the bathand converting the dross into an antimonial zinc-bearing metal together with a discard slag, returning the said metal to the process for retreatment with further quantities of impure metal entering the process,A utilizing the zinc chloride fusion from the bath for treating further quantities of dross, chloridizing the bath to convert'the zinc content thereof into zinc chloride, and reusing the moreimpure portions ot the zinc chloride for treating further zinc-alkaline-reacting metal-bearing metalbaths.

8. The prcess for treating an `impure alloy'l -of lead or tin containing antimony which comrecovering zinc from the said dross and utilizing the zinc so recovered in the treatment of additional impure ailoy, treating the partially reiined zinc-containing bath with a sucient quantity of an alkaline-reactingV metal to remove the remaining antimony from the bath, eecting a separation from the bath of an antimonial alkaline-reacting metal zinc-bearingdross, removing residual alkaline-reacting metal from the bath by treating the latter With zinc chloride, and treating the resulting bath to remove residual zinc from the bath.

9. Illlhe process for rening an impure alloy of lead or tin containing antimony which comprises partially removing the antimony by zinc while leaving residual zinc in the alloy, separating drosses and crusts therefrom, treating the zinccontaining bath with an alkaline-reacting metal to effect further removal of antimony, removing the alkaline-reacting metal dross from the bath. treating both bath and dross with zinc chloride to 'effect separation of alkaline-reacting metal a 1o. 1n the .art of derinumomzing alloys of1ead and tin with alkaline-reacting metal reagents,

the improvement which consists in fusing the alkalme-reacting metal dross with zinc chloride thereby freeing the heavy metal content of the dross from alkaline-reacting metal and eliminating the latter as a. slag, and returning the heavy metal so obtained to the process for deantimog nization with alkaline-reacting metal reagent. JESSE O. BE'ITERTON.

YURII E. LEBEDEFF. 

